class Person {
  String name;
  int _age;
  String? sex;

  //简写必选参数写法
  Person.ass(this.name, this._age, this.sex);
  //简写可选参数写法
  // Person(this.name, this.age, {this.sex});

  show() {
    print('我是$name,我$_age岁了, 性别为$sex');
  }
}
